I tried making a city of one-way streets but it's impossible to get good service coverage. A crime-filled house could be right next to a police station but will never be visited by police because the car goes the opposite direction. I guess the second best thing to do is to just do it for the industrial section.
Yeah, it goes by actual travel distance, not a radius. Are you using long rectangular blocks? I had noticed this issue and found it was a lot better when sticking with small square blocks (e.g. 8x8 or 10x10). If the car has a 100 cell travel allowance, for example, and it has to go around a 40 cell block to get in the other direction, it's used up its distance before it can even get past its starting point.
One way around this unwanted travel distance, sticking with long rectangle blocks, is to add opportunities for U-turns with smaller streets (or highway ramps) crossing the middle of your blocks. Just stagger them so they don't create 4-way intersections (lights).
The AI doesn't really use lanes very well, so one-way streets aren't as effective as they are in real life. I think there's more potential in using smaller side streets and ramps as your "lanes", that way you can design exactly how things should go.
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I've been having a ton of fun with the intersection tool for building repeatable tiles. I have a save where I'm pretty far along in the game (so everything's unlocked) and I've wiped out the centre so I can lay down the prefab tiles and see how things fill in. I had a pretty good one which created horizontal 6-lane roads and elevated vertical highways for the whole length of the city, all filled in with appropriate ramps. I messed up my ramp design though and wound up with too many left turns close together which created bottlenecks even though there were no lights. Back to the drawing board.